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    SubjectRe: RT patch acceptance

    * Andi Kleen <ak@muc.de> wrote:

    > [...] Even normal kernels must have reasonably good latency, as long
    > as it doesnt cost unnecessary performance.

    they do get reasonably good latency (within the hard constraints of the
    possibilities of a given preemption model), due to the cross-effects
    between the various preemption models, that i explained in detail in
    earlier mails. Something that directly improves latencies on
    CONFIG_PREEMPT improves the 'subsystem-use latencies' on PREEMPT_RT.
    Also there's the positive interaction between scalability and latencies
    as well.

    but it's certainly not for free. Just like there's no zero-cost
    virtualization, or there's no zero-cost nanokernel approach either,
    there's no zero-cost single-kernel-image deterministic system either.

    and the argument about binary kernels - that's a choice up to vendors
    and users. Right now PREEMPT_NONE is dominant, so do you argue that
    CONFIG_PREEMPT should be removed? It's certainly not zero-cost even on
    the source code, witness all the preempt_disable()/preempt_enable() or
    get_cpu()/put_cpu() uses.

    Ingo
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